Brake calliper with wear compensation

ABSTRACT

A brake calliper for a disc brake comprises a yoke carrying a pair of opposite brake pads and an electric actuating mechanism connected to the yoke, the actuating mechanism engaging a displaceable support member for displacing the brake pads towards and from each other. The actuating mechanism is driveable over a first range of rotations as well as over a second range of rotations, one of which ranges being for displacing the pads towards and from each other for exerting a braking effect on an associated brake disc, and the other range of which being for wear compensation of the pads.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is related to a brake calliper for a disc brake,comprising a yoke carrying a pair of opposite brake pads and anactuating mechanism connected to said yoke, said actuating mechanismengaging a displaceable support member for displacing the brake padstowards and from each other, wherein the actuating mechanism isdriveable over a first range of rotations as well as over a second rangeof rotations, one of which ranges being for displacing the pads towardsand from each other for exerting a braking effect on an associated brakedisc, and the other range of which being for wear compensation of thepads.

Such a brake calliper is known from GB-A-1 303 133.

2. Description of Related Art

In service, the brake pads gradually wear down which means that thescrew mechanism will have to be rotated over more revolutions before thedesired braking effect is obtained. From a point of view of proper brakebehaviour, it is however desirable to maintain a desired air gap betweenthe brake pads on the one hand, and the brake disc on the other hand. Asan example, a desired air gap of about 0.2 mm is usually preferred.

Due to wear however, the air gap may become much larger, e.g. in theorder of about 20 mm, and therefore a larger stroke will be required toengage the brake disc. Such magnitude of the air gap is less desirable,as it impairs the proper functioning of the brake.

Said prior art actuator comprises a ramp-raceway mechanism, which allowsa predefined maximum axial travel of the brake pads. Once this maximaltravel is reached, a screw-threaded compensator can be activated fordiminishing the play.

SUMMARY OF THE INVENTION

Said ramp-raceway mechanism as well as the compensator is activated by arotational movement in one and the same direction. The controlpossibilities of said actuator are therefore limited: the compensatorcan only be activated after a predefined amount of play has beenreached. The object of the invention is to provide an actuator of thiskind, which can be controlled in a more flexible way. This object isachieved in that the first range of rotations has a starting rotation inone rotating direction, and the second range of rotations has a startingrotation in the opposite direction.

According to an important aspect of the invention, the actuators arecontrolled independently from each other.

By means of a control device which may control the compensating andnormal braking actions, it is possible to start a compensating actionfor compensating brake pad wear, independently from the normal brakingactions.

Generally, the wear compensation will only be activated once thedeviation from the ideal air gap has become too large. However, saidcompensation will not occur in an automatic, unavailable way, but can becontrolled as desired, i.e. after a small or large wear increment in theair gap. In summary, the actuating mechanism is rotatable over a firstrange of rotations for obtaining a braking effect, and over a secondrange of rotating for obtaining a compensation effect.

The electric actuating mechanism only to a limited extent will be drivenover the second range of revolutions, e.g. in the order of 10,000cycles. In contrast, the first range of revolutions, which determinesthe braking action, will be used in the order of 1.000.000 cycles, inthe presence of relatively high loads. By selecting two different rangesfor these different circumstances of actuation, the actuating mechanismcan be adapted better to the requirements of reliability andcost-effectiveness.

According to a preferred embodiment, the actuating mechanism comprisestwo actuators, one actuator being for displacing the pads towards andfrom each other for exerting a braking effect, and the other actuatorbeing for wear compensation of the pads.

These actuators can be selected on the basis of the loadings and cyclesto be expected. Preferably, they are driven by a single drive part.

In order to be able to withstand the high number of braking cycles, thesingle drive part is a rotatable drive part which engages thedisplaceable support member by means of a first actuator comprising aramp raceway mechanism, which ramp raceway mechanism provides a linearmovement of the displaceable support member over a first range ofrotations, and a compensation movement of the displaceable supportmember over the second range of rotations.

A ramp raceway mechanism represents a sturdy and reliable means, fit forperforming relatively small displacements in a high cycle dutyenvironment. Relatively large displacements will not have to be dealtwith by this mechanism, having regard to the compensation movement ofthe displaceable support member which compensates for the wear of thebrake pads.

The ramp raceway mechanism may have a locking position, from whichposition a linear movement of the displaceable support member away fromthe rotatable part is obtained in response to a rotation in a firstdirection, and from which position a locking of the displaceable supportmember with respect to the rotatable part is obtained in response to arotation in the opposite direction.

Furthermore, the displaceable support member may engage a secondactuator comprising a nut, which nut engages the rotatable part by meansof the ramp raceway mechanism, and a screw which is connected to one ofthe brake pads and engaging the nut by means of screw threads whichprovide for a brake pad wear compensation displacement of the screw uponrotation of the nut from its locking position with respect to therotatable part of the motor in response to said rotation in oppositedirection.

In this embodiment, the wear compensation displacement is obtained bymeans of the relative rotations between the nut/screw mechanism. Suchmechanism is particularly fit for providing large displacements. On theother hand, it is not necessary for this mechanism to withstand highcycle duties, as it will be activated much less than the brake mechanismand will not be used for effecting a braking action.

The nut engages the housing, connected to the yoke, by means of aone-way locking mechanism which locks the nut against rotations over thefirst range, and which allows rotations over the second range; forinstance, the nut engages the housing by means of a ratchet pawlmechanism.

According to a preferred embodiment of the ramp raceway mechanism, therotatable part and the displaceable support member have facing radialsurfaces, each comprising three ramps, a roller being clamped betweeneach opposing pair of said ramps.

Each ramp at its lowest region has a stop for locking the associatedroller against further rotations. It is also possible to connect bothparts in a different way, e.g. by means of pegs or ridges.

In order to obtain reliable information concerning the air gap betweenair pads and brake disc, it is desirable to establish the point ofcontact between said components. To that end, preferably one of thebrake pads is connected to a load cell.

Alternatively, the measurement can be carried out optically.

Once the load cell establishes a loss of contact between brake pads andbrake disc, the count of revolutions of the actuator is started. Thedifferences from said starting point up to the point of the restposition then provides the desired information concerning the air gap.

Preferably, the actuating mechanism comprises an electric motor.

The invention is furthermore related to a method for operating the brakecalliper, comprising the steps of

monitoring the rotary movement of the actuating mechanism in the rangeof rotations for displacing the brake pads towards respectively fromeach other for exerting a braking effect on an associated brake discrespectively releasing said braking effect,

comparing an actual value related to the maximal number of rotations insaid range of rotations with a threshold value,

controlling the actuating mechanism so as to make it to rotate outsidesaid range of rotation, in order to compensate for wear, once the actualvalue has become larger than the threshold value.

Finally, the invention is also related to an actuator in general,comprising a frame carrying two members which can be brought into andout of mechanical contact with each other and an actuating mechanismconnected to said frame, said actuating mechanism engaging adisplaceable support member and being driveable over a range of rotatingfor displaying the members towards and from each other. Such actuatormay be used in the brake calliper as described before, but alternativelyalso in a mechanical clutch.

According to the invention, for wear compensation of said elements, theactuating mechanism is also rotatable outside said range of rotationsfor displacing the members towards and from each other. For instance,the wear of the clutch plates may be compensated for in this way.

BRIEF DESCRIPTION OF THE DRAWINGS

Subsequently, the invention will be explained with reference to anembodiment of the electromechanical brake with wear compensation asshown in the figures.

FIG. 1 shows a side view, partially in cross-section, of theelectro-mechanical brake according to the invention.

FIG. 2 shows a cross-section according to II—II in FIG. 1.

FIG. 3 shows a detail about the ramp raceway mechanism.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The brake calliper shown in FIG. 1 comprises a housing 1 connected to ayoke 2. The housing contains an electric motor 3, the stator 4 of whichis connected to the housing 1, 29, and the rotatable part 5 of which issupported on support piece 6. Support piece 6 is rotatably supported inthe housing by means of bearing 7 as well as four-point contact bearing8. This bearing 8 may have asymmetric working lines.

Support piece 6 is part of a first mechanical actuator 32, which engagesa displaceable support member 10 which carries one of the brake pads 11.The other brake pad 12 is connected to the yoke with possibleinterposition of load cell 13.

The displaceable support member 10 furthermore engages a secondmechanical actuator 33, which comprises a nut 14 which by means of screwthread co-operates with screw 15. Screw 15 has a head 16 at its sidewhich emerges from the screw 15, onto which head the brake pad 11 issupported. By means of a flexible bellows 17, the space containing theactuator and the electric motor 3 is sealed with respect to the outside.

For effecting a braking movement of the brake pads 11, 12, i.e. amovement towards each other, the first actuator 32 comprises a rampraceway mechanism. To that end, rotatable support piece 6 has a ring 18which has a first set of three ramps 19. Furthermore, displaceablesupport member 10 has a ring 20 which also has a set of three ramps 21.Between the ramps 19, 21, rollers 22 are held under pretension by meansof spring 23 which on the one hand bears against ring 18, and on theother hand against pulling member 24 connected to displaceable supportmember 10.

Upon rotation of the rotatable part 5 of electric motor 3 over a firstrange of rotations, i.e. in the figures shown according to a right handturn, the distance between ring 18 of rotatable support piece 6 and ring20 of displaceable support member 10 is increased due to the rollingmovement of the rollers 22 over the ramp raceways 19, 21. In FIG. 1,displaceable support member 10 is thereby translated to the left,pressing the brake pads 11, and 12 towards one another for obtaining abraking effect with respect to a brake disc (not shown) accommodatedbetween them.

Generally, in an ideal situation, the distance over which the brake pads11, 12 have to be moved towards one another, is small, e.g. in the orderof 0.2 mm. However, as soon as wear of the brake pads takes place,gradually this distance becomes larger leading to less favourablebraking behaviour due to for instance longer response times. Moreover,the ramp raceway mechanism in question can only accommodate translationsup to a relatively small maximum distance, which means that aftersomewhere has taken place, compensation must take place.

In the brake calliper as shown in the figures, brake pad wearcompensation is effected by means of the second mechanical actuator 33,comprising a screw 15 and nut 14. This nut forms an integral piece withdisplaceable support member 10. As shown in FIG. 3, the ramp raceways 19and 21 each terminate in a locking part 25 respectively 26. In a restposition of the brake calliper, the rings 18, 20 have reached such aposition that the rollers 22 are clamped between the locking parts 25,26. Upon further rotation of the rotatable support piece 6 by theelectric motor 3 in left hand direction, ring 18 and thereby nut 14 isalso rotated in left hand direction. Thus, nut 14 exerts a translationaleffect to the left on screw 15, whereby brake pad 11 is moved towardsbrake pad 12 for compensating the wear which has occurred. After wearcompensation, the first actuator 32 is in the desired position foreffecting a braking action, now starting from a desired, relativelysmall air gap.

In order to ensure that nut 14 only rotates in left hand direction, asseen in FIGS. 1 and 3, it has a ratchet teeth 26 at its circumference,which co-operate with correspondingly shaped pawls 27. Pawls 27 are heldunder pretension against the ratchet teeth 26 by means of flexibleelements 28, which are held clamped within the ring part 29 of thehousing 1. The pretension in combination with the geometry of thepawl-ratchet mechanism determines the torque required for activation ofthe second actuator.

As a further possibility, the brake calliper comprises a sensor 30having pulse rings which register the amount of rotation of therotatable support piece 6. On the basis of information obtained fromthis sensor 30, the electric motor 3 can be controlled in such a waythat the desired braking action is obtained. This sensor may serve basicfunctions such as giving information wear compensation, maintenanceindication, brake force feedback (ABS), traction control and for vehicledynamic functions.

Rollers 22 are accommodated in a cage 31, so as to keep them in theirproper position with respect to each other and with respect to the rampraceways 19, 21.

It is observed that the second actuator could also be operated manually.

What is claimed is:
 1. A brake calliper for a disc brake, comprising: ayoke; a pair of opposing brake pads supported by said yoke; an actuatingmechanism; a displaceable support member; wherein the actuatingmechanism is rotated through a first range of rotations, the first rangeof rotations having a starting rotation in one direction to displaceeach of said pair of opposing brake pads towards and away from eachother to exert a braking effect on said disc; and wherein the actuatingmechanism is rotated through a second range of rotations having astarting rotation in a direction opposite to said first range ofrotations, to move each of said pair of opposing brake pads toward eachother, incremently, to compensate for reduced brake pad thickness due towear.
 2. A brake calliper according to claim 1, wherein the actuatingmechanism comprises two actuators, a first actuator to displace each ofsaid pair of opposing brake pads towards and away from each other toexert a braking effect, and a second actuator to move each of said pairof opposing brake pads toward each other, incrementally, to compensatefor reduced brake pad thickness due to wear.
 3. A brake calliperaccording to claim 2, wherein the first and second actuators have acommon drive part, the first actuator is activatable by rotation of saiddrive part in one direction, and the second actuator is activatable byrotation of said drive part in the opposite direction.
 4. A brakecalliper according to claim 2, wherein the first actuator and the secondactuator are controlled independently from each other.
 5. A brakecalliper according to claim 1, further comprising: a ramp racewaymechanism; and wherein the actuating mechanism comprises a rotatabledrive part which engages the displaceable support member by means of theramp raceway mechanism to provide a linear movement of the displaceablesupport member due to a first rotation, and a compensation movement ofthe displaceable support member due to a second rotation.
 6. A brakecalliper according to claim 5, wherein the ramp raceway mechanism has alocking position, from which position a linear movement of thedisplaceable support member away from the rotatable part is obtained inresponse to a rotation in a first direction, and from which position alocking of the displaceable support member with respect to the rotatablepart is obtained in response to a rotation in the opposite direction. 7.A brake calliper according to claim 6, wherein the displaceable supportmember engages the second actuator comprising a nut which engages therotatable part by means of the ramp raceway mechanism, and a screw whichis connected to one of the brake pads and engaging the nut by means ofscrew threads which provide for a brake pad wear compensationdisplacement of the screw upon rotation of the nut from its lockingposition with respect to the rotatable part in response to said rotationin opposite direction.
 8. A brake calliper according to claim 7, whereinthe nut engages a housing, connected to the yoke, by means of a one-waylocking mechanism which locks the nut against rotations for obtaining abraking effect, and which allows rotations for obtaining a compensationeffect.
 9. A brake calliper according to claim 8, wherein the nutengages the housing by means of a ratchet pawl mechanism.
 10. A brakeactuator calliper according to claim 5, wherein the rotatable part andthe displaceable support member have facing radial surfaces, eachcomprising three ramps, a roller being clamped between each opposingpair of said ramps.
 11. A brake calliper according to claim 10, whereineach ramp at its lowest region has a stop for locking the associatedroller against further rotations.
 12. A brake calliper according toclaim 10, wherein a spring is provided for preloading the ramps and therollers.
 13. A brake calliper according to claim 5, wherein therotatable part is supported with respect to the housing by at least oneangular contact bearing.
 14. A brake calliper according to claim 1,wherein one of brake pads is connected to a load cell.
 15. A brakecalliper according to claim 5, wherein the rotatable part is a componentof, or is driveably connected to, an electric motor, the electric motorhaving a stator which is connected to the yoke.
 16. A brake calliperaccording to claim 1, wherein a sensor is provided for sensing therotary movement of the actuating mechanism.
 17. A brake calliperaccording to claim 16, comprising a control unit for controlling anelectric actuating mechanism on the basis of signals from the sensor anda brake signal.